This circuit was found in a 90s Popular Electronics. It is used for the acoustic transmitters of 40 kHz, as several found in this section. Transistors support current equivalents.
This circuit was found in the Radio Electronics magazine of May 1990. The transistor is...
The circuit is from an 80's publication, but the components are current, only special type diodes...
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...